In documenting the emergence of cosmic chemical complexity, of a cosmos replete with large carbon-based molecules emerging from a simple soup of hydrogen and helium, astronomers have shifted the notion of the big bang from one relating to the origins of the physical universe to the story of a biological big bang. The tale is the crowning achievement of twentieth-century cosmology and astrophysics, joining the birth of the visible universe, of time and space, from the quantum nature of atoms to the grand architecture of the cosmos.

It's about developing a universal understanding of life and its origins and cosmic distribution. It's about understanding how Darwinian evolution can be extended, or embedded, in the breadth of cosmic evolution extending from the origin of the elements in stars, to cosmic chemical evolution, to the emergence of solar systems, and—of most interest to us— to the origins of life in this cosmic context.

The story of this week's Episode 6 is also related in brilliant book, The Stardust Revolution, by Jacob Berkowitz, that traces of our origin in the stars. Twentieth-century astronomy was dominated by astrophysics, the search for the physical origins and structure of the universe. Now a new breed of scientists—astrobiologists and astrochemists—are taking the study of life into the space age. Astrobiologists study the origins, evolution and distribution of life, not just on Earth, but in the universe. Today's scientists aren’t probing the universe’s physical structure, but rather its biological nature. Evolutionary theory is entering the space age.

Astrobiologists are literally tracing the natural history of the cosmos from the Big Bang to our bodies. They’re making the evolutionary links from atoms formed by stars, to the molecules of interstellar space and the emergence of living planets. The paragraphs that follow are excerpts from the book.

When we seek our origins, we follow the tree of life that connects us not just back to distant ancestors on Earth but also to everything else in the cosmos, allowing us to develop an understanding of life as an emergent weave from the atoms forged in stars to the birth of a child. At the heart of this pursuit, the tracing of our family tree back to a time before the first life on Earth or even before the Earth itself, is a truly extreme genealogical question: What is life?

The story of the epic journey of our origins, the tracing of our family tree— doesn't start with thinking about the origin of species but rather with thinking about the origin of stars. To understand the cosmic context of our origins, of cosmic evolution, is to trace the genealogy of stars back to the dawn of time. The long-asked cosmic question “Are we alone?” has been transformed into the extreme genealogy question “How are we connected?” Perhaps in the not-too-distant future, the question may be “How are we related?”

Starting with the story hydrogen we come not so much to understand this tiniest atom but to understand the essence of the entire cosmos. The doorway to understanding the full complexity and expanse of the observable universe is through its simplest atomic constituent, back tothe very beginnings of time, when hydrogen was just about the only elemental word the newborn universe could utter. In the beginning there were no atoms or molecules. It was an unpromising scenario for the formation of complex structures like galaxies; black holes; stars; planets; nuclear, atomic, and molecular systems; and living organisms.

At its first breath , the cosmos was unrecognizable to everyone except particle physicists. The universe emerged with such energetic fury that only the fundamentally indivisible particles , the quarks and electrons, could survive intact, bathed in a sea of intense radiation. The newborn cosmos was dense, gassy, and unimaginably hot, too hot for matter to stick together; there was nothing solid or liquid. Particles collided with such force that they ricocheted rather than bonded or fused.

But as the universe expanded, creating time and space, it also cooled . After just one second, slightly less energetic quarks congealed into the more familiar neutrons and protons that form the nuclei of atoms. Within three minutes (astrophysicists clock it to about two hundred seconds, less time than it takes most of us to shower), the growing cosmos’ temperature had fallen to under two billion degrees Fahrenheit. At this temperature, the cosmos experienced its first burst of nuclear building, or big-bang nucleosynthesis.

Though most protons stayed single, a quarter by mass of all the baryonic matter (the stuff we see as matter, excluding dark matter) was forged into helium nuclei—two protons and two neutrons—and tiny amounts of lithium and beryllium, the next two elements on the periodic table. After fifteen minutes, this first act of heated creation was over.

But the growing universe was still so hot, and thus energetic , that these nuclei couldn't hold onto a single electron; they were fully ionized. For about four hundred thousand years, says Dalgarno, the universe “coasted along” in this ionized state, expanding and cooling. Then, like a baby's first smile , something truly new happened in the life of the cosmos: the first fully formed atoms were born.

The expanding cosmos had cooled enough that, one by one, across space and time, when a positive nuclei and an electron collided, they didn't deflect like colliding billiard balls but stayed bonded together to form the neutral atoms of hydrogen and helium. Astrophysicists call it the Recombination Era; though the term recombination is a misnomer, since these negative and positive particles were never previously combined. With neutral atoms came a crucial evolutionary stage.

The infant cosmos took its first chemical baby steps through a series of collisions between helium and hydrogen atoms energized by bountiful electrons and photons, most lone, neutral hydrogen atoms joined to become molecular hydrogen. These were the cosmos’ first atomic bonds, and with them came the introduction of a new cosmic form: the molecule. With this step, the cosmos gradually went dark.

Molecular hydrogen is a gassy curtain, opaque to visible wavelengths of light. To the human eye, the universe was completely dark for its first hundred million years— hence the Recombination Era's other name, the Dark Ages. But this epoch was also the dawn of chemistry. Molecular hydrogen paved the way for the creation of a vastly expanded cosmic alphabet, one that could articulate the language of life.

“The introduction of the neutral hydrogen molecule was a crucial step in the evolution of the universe,” says Alexander Dalgarno, the "father of molecular astrophysics" and a physicist at the Harvard-Smithsonian Astrophysical Observatory and director of the Institute for Theoretical Atomic and Molecular Physics. It was only out of darkness that light could emerge. It was only because the cosmos went dark that the next evolutionary step could take place. Star formation depends on atoms’ and molecules’ abilities to radiate away the heat from gravitational collapse, and molecular hydrogen was the antifreeze of the early universe. Without it, the first stars couldn't be born almost two hundred million years later, in the era of cosmic dawn, now one of the most sought-after epochs in cosmic history.

With the birth of the stars came an exponential bump in the nature of cosmic chemistry, the forging of a panoply of elements from carbon to uranium. These elements, in turn, found partners to create previously unseen types of unions, and they filled the universe with a new vocabulary of molecules such as carbon monoxide and formaldehyde— the building blocks of organic chemistry —and minerals, including sandy silicon dioxide , the crystalline beginning of rocky planets.

Comments

I wish he would stick to facts and not give credit, where credit is not due. Like the guy who discovered black holes? 'Well, if there are white stars, there must be black stars' is not a discovery, but an assumption. There were no famous brownies in astronomy. No brain power there.